Using neonatal swine as our animal model of sudden infant death syndrome (SIDS), we will investigate (using both acute and chronic preparations): 1) postnatal differences in innervation of the heart by vagal and postganglionic sympathetic motoneurons, 2) the role of cardiac arrhythmias and the effects of selected visceral afferent stimulation in the etiology of SIDS, 3) the effects of different combinations of autonomic denervation of the heart on survival. In addition, chronic animals, either sham operated or denervated, will be studied under different conditions including such stresses as feeding, temperature changes or hypoxia. These denervation studies will allow the determination of the importance of innervation postnatally. The results of the experimentally induced laterality of sympathetic and/or vagal dominance will verify the importance of balanced innervation of the heart. In the acute preparation we will also examine the effects of denervation on: 1) the ventricular fibrillation threshold and 2) responses to stimulation of visceral afferents, e.g., cardiopulmonary, J-receptor and chemoreceptor. Finally, to examine postnatal maturation of autonomic regulation of the heart and, therefore, of times of greatest susceptibility to arrhythmias, we will obtain motoneurons in the ventrolateral nucleus ambiguous in order to determine: 1) their changing pattern of activity with age, 2) their responses to afferent inputs. and 3) whether their evoked responses are age-related. These experiments will also supply the needed information concerning the role of cardiac arrhythmias in SIDS as well as document the suitability of neonatal swine as an animal model for this disease. The chronic animals will be prepared under sterile operating conditions; vascular access ports will be implanted for blood sampling and pressure measurements while fine wire electrodes will be inserted into the diaphragm for monitoring of respiratory function; the EKG will be recorded from needle electrodes. Acute experiments will be performed under Saffan anesthesia. The aforementioned chronic and acute experiments should supply much needed information regarding the importance of changing autonomic regulation of the heart in the etiology of SIDS.